A centrifugal casting process is a casting process of forming a casting in such a way that centrifugal force is applied to molten metal by rotating a mold. In other words, this is a process in which centrifugal force may act uniformly on the entirety of the mold by the rotation of the mold so that the casting process may be performed while pressure is applied to the molten metal.
Since the mold is rotated at high speed of 300 to 3000 RPM, it is possible to obtain a dense structure by the centrifugal force. In addition, it is possible to produce a casting of a high quality through the separation of impurities using a difference in specific gravity. Thus, the centrifugal casting process is being widely applied to circular components including a pipe, a water pump pulley, a damper pulley hub and the like, as well as components, such as an inner core, having various shapes.
However, the centrifugal casting process is problematic in that RPM may not be increased beyond a certain level, due to practical problems including the problem of equipment, the spreading of molten metal and the like.
Therefore, when casting is performed, the RPM may not be sufficiently high.
If the RPM is low, the casting is affected by the gravity and the centrifugal force, as illustrated in FIG. 1. In this case, since force is intensively applied in the direction of a resultant force of the gravity and the centrifugal force and a certain part is subjected to less force, it is difficult to secure the castability due to a difference in casting pressure, and a difference in physical properties may occur.
FIG. 2 illustrates a water pump pulley made of a single material by centrifugal casting. As shown in portion A of FIG. 2, a non-molded part may occur because of the directivity of pressing.
On the one hand, in an aluminum casting process for achieving a reduction in weight, it is advantageous to make one product using two different materials by casting. Therefore, a current trend in a casting field is towards hybrid casting of metal.
That is, a required material may be used only for a required part so that the required material can serve as a functional material, thus realizing a reduction in cost and weight.
For example, a retainer component of a transmission requires abrasion resistance on a surface thereof. Thus, if the surface of the component is made of K14 by casting and an interior thereof is made of ADC12 by casting, it is possible to realize a reduction in cost and weight.
The foregoing is intended merely to aid in the understanding of the background of the present disclosure, and is not intended to mean that the present disclosure falls within the purview of the related art that is already known to those skilled in the art.